1. Field of the Invention
This invention lies in the area of motorized bell systems and, in particular, an electric motor drive system for ringing a cast bell having automatic startup capability.
2. Description of the Prior Art
Motorized systems for swinging large cast bells have been known in the art for some time. The assignee of this invention has used a system comprising a single phase 1140 RPM, 208 VAC drive motor, with power transmission from the motor to the bell via a motor mounted sprocket, linked chain and wheel attached to the bell yoke. The system also includes two snap action switches which provide control to the motor, namely a duration switch and a direction switch. The duration switch determines the duration or angular arc through which the bell swings, while the direction switch senses the bell swing direction and reverses the position of its switch contact so as to provide energization of the motor in the direction of bell swing through the duration arc. In this manner, the motor drive and the bell momentum aid each other. When the bell has gained enough momentum to increase the arc of travel to an extent that the duration switch deenergizes the motor power, the bell soon reaches the peak of its arc and reverses its direction and starts to fall, such that the direction switch changes position. After the bell has fallen enough for the duration switch to again energize, the motor drives the bell in its new direction.
In the above system, it is noted that the duration switch provides power through an angle which is less than the arc through which the bell swings. This is similar to a clock, where power is applied to the clock pendulum for only a small portion of the pendulum travel. Of course, it requires far less power to maintain the bell in motion once it has acquired momentum, than to start it in motion. With a pendulum clock, this problem is circumvented by initially placing the pendulum in motion manually. However, for an automatic bell system, particularly for a heavy cast bell, manual starting is generally not feasible and motorized startup is required. At initiation of bell swinging, power is supplied until the motor stalls or the duration cam opens on a partial swing, at which point the bell stops and swings downward toward the rest position. This change of direction is sensed and power is caused to be applied in the reverse direction. The cycle repeats itself until the bell has achieved a normal swing arc, or condition. When swinging in its normal arc, power is disconnected when the bell passes the duration angle in its upward travel. Inertia causes the bell to travel onward until it stops and reverses its direction and power is not reapplied until the bell falls back to the duration angle limits. Thus, the change in direction does not cause application of power at that moment, but rather power is only applied again when the bell has fallen to the duration limit.
Under certain circumstances, the above-described cycle is prone to failure because the bell does not return to a position within the duration angle, or "duration window". The circumstance can arise, for example, due to high friction bearings, which prevent the bell from returning to a downward position which is within the duration limits. In a similar manner, a bell with a yoke pivot point placed very low, such as is found in bells with yokes designed for rope pull, may have instances where the bell comes to rest outside the range of the duration angle, and hence fails to restart. This circumstance can also be promoted by high wind conditions, ice formation, and other naturally occurring conditions.
A compromise solution to the restart failure problem is to apply swinging power for a greater number of angular degrees than a normal swing rate requires. This solution is obtained by providing a larger duration angle, thus giving the bell a greater chance of coming to rest within the duration window where power will be applied at the next startup. However, this solution can be implemented only to a certain extent, and is not very practical because the bell no longer swings at its normal pendulum rate but rather is driven at high speeds and has the characteristic of crashing from side to side. In other words, the compromised start condition is obtained at the sacrifice of the bell drive, or duration window. Indeed, carrying this solution too far results in the bell turning completely over.